Tank-roof structure



April '15, 1930.

c. F. H. BOHNHARDT TANK ROOF STRUCTURE Filed Dec. 5, 1928 2 Sheets-Sheet '1 April 15, 1930. c. F. :H. BOHNHARDT Patented Apr. 15, 1930 UNITED STATES PATENT OFFICE CHARLES F. H. BOHNHARDT, OF LYNWOOD, CALIFORNIA, ASSIGNOR TO JULIAN A.

CAMPBELL OF LONG BEACH, CALIFORNIA TANK-ROOF STRUCTURE Application filed December 5, 1928. Serial No. 324,040.

This invention has to do generally with storage tanks and relates more particularly to floating and expansion roof construction for tanks in which petroleum oils or the like 5 are stored.

It may be stated primarily that a general purpose for the use of floating roofs in oil storage tanks is to prevent the expulsion of vapors from the upper space in the tank above the liquid level therein as liquid is being pumped into the tank, and to prevent the intake of air into said space when liquid is withdrawn from the tank, the air serving to form, with the vapor, a combustible mixture. The floating roof thus operates by riding on the surface of the liquid and rising and falling with the liquid level so that at no time, under normal conditions, is a vapor space formed between the liquid and the roof.

Should the floating roof be directly exposed to the atmosphere, it is evident that during warm Weather the roof becomes abnormally heated, with the resultant heating of the liquid and increasing of its vapor pressure, the latter being especially true if the tank liquid contains unusually volatile constituents. In my co-pending application on air cooled floating roof, filed January 14, 1928, Serial No. 246,758, I have shown and described a type of weather roof to be erected over the floating roof in order to protect the latter, the space between roofs being open to the atmosphere to provide for air circulation in keepinv the floating roof desirably cool.

In anot er co-pending application entitled Liquid seal expansion roof, filed February 1st, 1928, Serial No. 251,195, I have described a tank structure in which a floating roof is dispensed with and an expansion weather roof used in its stead, the weather roof in this instance being spaced from the liquid level in the tank and adapted to float by virtue of vapor pressure on its under surface. The

5 floating weather roof in this instance has sufficient expansibility to accommodate changing conditions of pressure and volume during breathing of the tank. It may be noted however, that when the liquid level in the tank is low, there is considerable vapor space above said level and therefore when the tank is refilled, a great portion of this vapor must be forced out of the tank as it is impractical to construct a roof to take care of such volume increase.

It has now been found desirable, in certain instances where roofs floating on the liquid are used, to provide vents through the roof in order to insure against the formation of a vapor body above the liquid, and the loss of such vapor to the atmosphere through the seal between the roof and the tank. I have, therefore, provided the present tank structure in which this provision is made, and in addition have incorporated in a single structure numerous desirable features of the devices comprising the subject matter of the referred copending applications. More specifically, I provide a floating roof, suitably sealed with respect to the tank wall, and a weather expansion 'roof above the floating roof, the space between the roofs being closed to the atmosphere by suitable seal means between the roofs, and said space bein communicable with the tank liquid through vents in the floating roof. The space between roofs being comparatively small, and independent of the liquid level, under normal conditions the Weather roof has suflicient expansibility to take care of pressure and volume changes, especially since the floating roof is protected thereby. However, in the event the weather roof reaches its limit of expansion, the vapors may be passed to suitable containing means, it being noted that the volume of vapors which it is necessary toremove to reduce the pressure between the roofs, is comparatively small.

The various features and advantages of the invention will most readily and clearly be understood from the following detailed description of typical embodiments thereof, reference being had throughout the description to the annexed drawings, in which:

Figure 1 is a diagrammatic illustration of a preferred embodiment of my invention, the expansion roof sloping radially inward and having a center drain,

Fig. 2 is a fragmentary enlaged view of the seal construction shown in ig. 1;

Fig. 3 is an enlarged detail view of the pater drain seal generally indicated at D in Fig. 4 is a view similar to Fig. 1 showing a variational structure, in which the expansion roof slopes radially outward and has an outside drain;

Fig. 5 is a view similar to Fig. 2 of the seal structure employed in Fig. 3; and

Fig. 6 illustrates a variational form of liquid seal construction.

Referringfirst to Fig. 1, I have illustrated diagrammatically the usual oil tank T having a vertical cylindrical shell 10 within which liquid 11, such as petroleum oil, is contained, the liquid being introduced to the tank through inlet 12 and withdrawn through the outlet 13. I have provided a floating roof of suitable design, generally indicated at F, which is adapted to float on the liquid at all times, that is, irrespective of the amount of liquid contained within the tank. Above the floating roof and spaced therefrom at S, is a weather expansion roof E, this roof being vertically movable with respect to the floating roof F, and the space S between the roofs being closed to the atmosphere during this movement. A suitable seal generallyindicated at 14, is provided between the two roofs in order to maintain space S closed during the relative movement, the seal also embodying means for preventing the escape of fluid from the liquid body 11 between the shell and the floating roof.

It is to be understood that in its broad interpretation, the invention is in no way limited to/a floating and expansion roof having the specific construction of the types illustrated, and further, that the invention is not to be limited by the particular construction provided for maintaining a seal between the roofs and between the tank and the floating roof. Therefore, the invention broadly contemplates the use of any suitable floating roof, an expansion roof spaced above the floating roof and vertically movable relative thereto, the space between the roof being closed to the atmosphere and in communication with the tank liquid, and any suitable means for maintaining said space closed to the atmosphere during relative movement between'the. roof.

The floating roof F, in the illustrated forms, is made up of a plurality of basins or float units 15, shaped in plan to aflord their convenient arrangement within the tank, and joined to one another as at 16. Similar roof constructionis shown and described more in detail in the referred copending application on air cooled floating roof. It may be noted that the units are jointed at points above the liquid level, and consequently there is no tendency for liquid to leak through the roof.

The floating roof carries around its periphery a trough 18, the inner Wall 18* of which is joined to the outermost float units as at 19, this joint as well as the joint between the several float units being fluid tight. The outer trough wall 18 is spaced from the tank shell at 21, there being suitable means, as will later be seen, for forming a seal between the floating roof and the shell to prevent the escape of vapor from the tank through the clearance space. lVithin the tank and integral with shell 10 is an annular skirt 22 de-, pending from a horizontal portion 22 and extending downwardly within trough 18, preferably to a point near its bottom when the floating roof is in its upper-most position. Trough 18 is filled with liquid 23, for instance water having a small amount of non-volatile oil on its surface to prevent evaporation. It is seen that a liquid seal is maintained between the floating roof and the tank shell, said liquid seal preventing the flow of vapors from space 21 to the atmosphere when the roof is in its upper position.

Although any suitable form of vapor seal may be provided between the tank and floating roof, I have illustrated a preferred type which is particularly effective for the purpose set forth. The vapor seal embodies an annular sheet 24 spaced from the bottom of trough 18 and supported on seat 24. A roller 25 is mounted on the upper end of sheet 24 and is adapted to engage the tank wall at all positions of the floating roof, a roller, instead of a sliding contact between the tank and sheet 24 being provided to eliminate friction. Confined between plate 26', block 27, and the horizontal end portion 24 of the sheet is a pair of flexible flaps 28 of suitable composition, for instance rubber impregnated canvas, these flaps serving to engage the shell with suflicient tightness to prevent the escape of vapors into space 29.

It will be seen that should considerable liquid be removed from the tank causing the floating roof to fall to such an extent that the liquid seal maintained by skirt 22 in trough 18 becomes broken, sheet 24, in being submerged at its lower end in the liquid 23 and being in engagement with the tank at its upper end through the flexible flaps as de scribed, forms an additional seal that is effective regardless of the position of the floating roof. Seal means of this general character are described more in detail in United States Patent No. 1,597,046 issued August 24, 1926 to Joseph R. Baril and myself.

The preferred type of weather expansion roof 30 shown in Fig. 1, is inclined radially inward in order that rain water may drain to the center of the roof and thence to the bottom of the tank in a manner that I will presently describe. When in its lowermost position the expansion roof is supported on a frame work comprised of posts 31 and cross members 32 built up on the floating roof as illustrated. Guide posts 33 having footing on the floating roof extend vertically within pipes 34 mounted on the expansion roof, these members serving more or less to guide the expansion roof in its vertical movement, and to prevent relative horizontal displacement of the roofs.

The expansion roof has an outer annular skirt 35 which extends downwardly within trough 18 mounted on the floating roof, and serves to maintain a liquid seal between space S and the atmosphere. The extent of vertical movement of the floating roof from its lowermost position illustrated in Fig. 2 wherein the floating roof is shown resting upon wall 18 of trough 18, is determined by the vertical distance the expansion roof may move upward and skirt 35 yet maintain a liquid seal trough 18. Conversely, the limiting height above the floating roof to which the expansion roof may rise may be predetermined in accordance with the particular depth given trough 18 and the length of skirt 35. I The inner wall 18 of the trough preferably extends upward a greater distance than the outer wall 18 in order that should the tank be filled to overflowing, the overflow will occur outside of the tank rather than on the floating roof.

Openings or vents 37 are provided in the floating roof in order to establish communication between the liquid body 11 and the space between the roofs, this space therefore being filled at all times with vapors, mainly volatile constituents of the liquid, the pressure exerted by the vapor being dependent upon the temperature of the liquid and its volatile content. It may be stated that the vapor pressure necessary to float the expansion roof is but a few inches of water, and therefore no serious back pressure is exerted on the tank.

As a typical means for draining water from the weather roof I have provided a pipe 38 welded at 38 to the apex of the floating roof, pipe 38 opening at its lower end into a container 40 welded to the pipe at 40. A cup 41 is joined to the floating roof at 41 a conduit or hose 42 leading from the bottom of the cup to the tank bottom. Container 40 has a plurality of openings 43 near its top, these openings permitting water discharged into the container through pipe 38 to overflow into cup 41, from whence it passes through conduit 42 to the bot-tom of the tank. It is seen that the liquid seal is maintained in cup 40 thus preventing the escape of vapors in space S through openings 43 and pipe 38 to the atmosphere.

The variational form of the invention shown in Fig. 4 is generally similar to that of Fig. 1, but differs in that the roof slopes radially outward to water receiving troughs around its periphery, and in that the liquid seal is somewhat altered to accommodate the change in the floating roof structure. In this form a comparatively shallow trough 45 is joined to the downwardly and outwardly inclined roof 46 around its periphery, the trough being adapted to rest on the floating roof when theexpansion roof is in its lower position as shown in Fig. 5. A relativelydeep trough 18 is mounted on the floating roof, as in the former instance, an annular sheet 47 carrying the vapor seal generally indicated at 47 being provided as before.

Instead of providing a skirt around the periphery of the expansion roof in this instance, I employ a seal ring 48 shaped as illustrated so that one leg 48 is submerged within the liquid in trough 18 and the other relatively short leg 48 depends beneath the liquid in trough 45. Therefore when the expansion roof raises above the floating roof, the seal ring, by virtue of its being submerged in both troughs maintains an effective liquid seal preventing the escape of vapors from space S to the atmosphere. The outer Wall 45 of trough 45 preferably extends higher than the inner wall 45', in order that rain water having drained from the roof to fill the trough will be prevented from overflowing on the floating roof.

In Fig. 6 I have illustrated a variational form of liquid seal, generally similar to that of Fig. 4 but providing, in addition, means for maintaining a liquid seal between the floating roof and the expansion roof when the latter is raised to an extent such that the liquid seal between the roof in the previous types would be destroyed. Seal ring 50 serves in this instance substantially the same purpose as that described for seal ring 48 in Fig. 5. Ring 50, however, is shaped at its lower end to form an annular hook 51, there being contained in the trough 18 and concentric with ring 50 a plurality of telescopic segments 52. These segments are provided at their upper and lower ends with hooks 52 the innermost segments being suspended from the ring 50 when the latter is carried upward by the floating roof a distance such that hook 51 engages the upper hook of the segment. The outer segment is similarly suspended from the inner segment when the expansion roof becomes raised a distance corresponding to the combined lengths of the segments. It will be understood, of course, that any suitable number of segments may be provided. The particular construction and use of these telescopic segments in liquid seals of this character is more fully described in the United States Patent No. 1,666,525 issued jointly to-Joseph R. Baril and myself on floating roofs and sealing means therefor.

It will be understood the drawings and description are to be considered merely as illustrative of and not restrictive on the broader claims appended hereto, for various changes in design, structure and arrangement may be made without departing from the spirit and scope of said claims.

I claim:

1. In a structure of the character described, a tank containing liquid, a floating roof adapted to float on the liquid, an expansion roof spaced above the floating roof, the space between said roofs being closed to the atmosphere and in communication with said liquid.

2. In a structure of the character described, a vertical shell containing liquid, a floating roof adapted to float on said liquid, an expansion roof spaced above the floating roof and vertically movable relative thereto, the space between said roofs being closed to the atmosphere and in communication with said liquid, and means for maintaining said space closed to the atmosphere during relative movement between the roofs.

3. In a structure of the character described, a vertical shell for containing liquid in varying amounts, a floating roof adaptedto float on said liquid and to rise and fall with the liquid level, an expansion roof spaced above the floating roof and vertically movable relative thereto, means for maintaining the space between the roofs closed to the atmosphere, and means for maintaining a seal between the floating roof and the tank to prevent exposure of said liquid to the atmosphere.

4. In a structure of the character described, a vertical shell for containing liquid in varying amounts, a floating roof adapted to float on said liquid and to rise and fall with the liquid level, an expansion roof spaced above the floating roof and vertically movable relative thereto, the space between said roofs being communicable with the liquid and closed to the atmosphere, liquid seal means between the floating roof and the shell, and liquid seal means between the roofs.

5. In a structure of the character described, a vertical shell for containing liquid in varying amounts, a floating roof adapted to float on said liquid and to rise and fall with the liquid level, an expansion roof spaced above the floating roof and vertically movable relative thereto, means for maintaining the space between the roofs closed to the atmosphere, means for maintaining a seal between the floating roof and the tank to prevent exposure of said liquid to the atmosphere, and means preventin relative horizontal displacement of the roo s.

6. In a structure of the character described, a vertical shell containing liquid, a floating roof adapted to float on said liquid, an expansion roof spaced above the floating roof and vertically movable relative thereto, the expansion roof sloping radially inward toward its center, the space between said roofs being closed to the atmosphere and in communication with said liquid, means for maintaining said space closed to the atmosphere during relative movement between the roofs, and means for draining li uid from the top of the expansion roof ownward through the floating roof and to the bottom of said shell.

7. In a structure of the character described, a vertical cylindrical shell containing liquid, a floating roof adapted to float on said liquid, an annular trough at the edge of said roof, an apron mounted on the upper end of the shell and adapted to extend downward into said trough, closure means between the trough and the inner wall of said shell, an expansion roof spaced above the floating roof and vertically movable relative thereto, the space between the roofs being communicable with the liquid beneath the floating roof, and an annular apron on said expansion roof and depending into said trough on the inside of the first mentioned apron.

8. In a structure of the character described, a vertical shell containing liquid, a floating roof adapted to float on said liquid, an expansion roof spaced above the floating roof and vertically movable relative thereto, the expansion roof sloping radially inward toward its center, the space between said roofs being closed to the atmosphere and in communication with said liquid, an annular trough mounted on the outer edge of the floating roof, an annular apron on said expansion roof and dependin into said trough to form a liquid seal etween the roofs, and liquid seal means for draining liquid from the center of the expansion roof downward through the floating roof to the bottom of said shell.

In witness that I claim the foregoing I have hereunto subscribed my name this 26th day of October, 1928.-

GHARLES F. H. BOHNHARDT. 

